1. Field of the Invention
The present invention relates to a light patterning device and method of using the same.
2. Background Art
A patterning device is used to pattern light. A static patterning device can include reticles or masks. A dynamic patterning device can include an array of individually controllable elements that generate a pattern through receipt of analog or digital signals. Example environments for use of the patterning device can be, but are not limited to, a lithographic apparatus, a maskless lithographic apparatus, a projector, a projection display apparatus, or the like. The following discussion involves patterning devices in lithography, but can be extended to the aforementioned apparatuses, as would become apparent to persons having ordinary skill in the art.
Currently, arrays of individually controllable elements can include various types of mirrors. For example, piston mirrors, single phase-step tilting mirrors, flat tilting mirrors, or hybrid mirrors combining tilt and piston actions.
However, these arrays cannot effectively emulate phase shifting masks because of intensity modulation constraints (e.g., unequal maximum amplitude of positive and negative light) and/or are inefficient when correcting telecentric errors.
Individually, piston mirrors have a pure phase modulation effect, but amplitude modulation can also be obtained by combining piston mirrors into one large pixel. This results in a loss of resolution as well as limits the ability in replicating the effect of assist features (e.g., features intended to improve lithography on a customer wafer, for example, optical proximity correction features, serifs, hammerheads, scattering bars, anti-scattering bars, etc.) smaller than the largest pixel. There is also significant throughput loss with this approach.
Tilting mirrors are used to produce different amplitudes of reflected light at an image plane and/or collected (captured) at projection optics, in a lithography system, for example. At different phases, an amplitude of reflected light, as seen at an image plane and/or collected at projection optics, is considered to have positive or negative light amplitude. For example, when a mirror is untilted (e.g., resting) light at the image plane and/or collected at projection optics is considered to have a positive amplitude with zero phase. During tilting of the mirror, there is an tilt angle at which no light is directed toward the image plane and/or is collected at projection optics, so the amplitude of the light at the image plane goes to zero. Then, as the mirror continues to tilt, out of phase light reaches the image plane and/or is collected at projection optics, which is considered to be negative amplitude light.
When imaging with tilting mirrors, there can be a telecentricity error. Telecentricity can occur during patterning on an object as a pattern goes into and out of focus, and causes an image being formed to move/shift slightly.
One type of tilting mirror, discussed above, is a single phase step tilting mirror (λ/4 phase step or λ/2 phase step; where λ is the wavelength of light or imaging wavelength), for example, proposed by Micronic Laser Systems of Sweden. This mirror can achieve an intensity modulation anywhere between about positive 50% and negative 50%. When at rest, no light enters a pupil of a projection system because, due to the step, half the light has a zero degree phase and the other half of the light has a 180 degree phase. As the mirror is tilted, light is captured or collected by the projection system, where a direction of tilt determines whether positive or negative light is captured or collected. Because of the symmetry of the single step mirror, equal amounts of positive and negative light can be captured or collected by the projection system. However, to correct for telecentric errors the one step mirror requires alternating the position of the step (right or left). This results in the dependence of the tilt angle sign on the position of the edge. This means that in order to achieve a given graytone with a particular mirror, the sign of the tilt angle needed will require knowledge of where the step is located, which creates an additional strain on the data path. In addition, mirror curling at the edges is likely to be exacerbated on the thinner side of the mirror and result in “tilt errors.”
An alternative tilting mirror, also discussed above, is a flat tilting mirror, which can achieve an intensity modulation anywhere between 100% positive phase intensity and 4.7% negative phase intensity. This limited negative phase intensity has proven to be a major limitation in emulating alternating phase shifting masks without significant light loss. By design, the space between these mirrors is typically as small and opaque as the fabrication process allows.
Therefore, what is needed is an array of individually controllable elements, where each individually controllable element when used in the array has better positive and negative intensity characteristics and/or allows for effective and efficient telecentric error correction and/or does not decrease the throughput.